Tips on Sewing Biothane?

[TomE]

I am starting to sew halters made from 2-3 layers of Biothane Beta 520 super heavy (3.5-4 mm thick) on a Cobra Class 4.  I am having problems with skipped stitches, mainly when backstitching 2-3 layers near hardware.  I am using a holster plate that allows me to stitch closer to a center bar buckle.  I did make small adjustments to the hook timing, following @Uwe's video on Youtube.  Thanks, Uwe!  The machine sews leather fine.

My current setup for Biothane is the Hennigan Precision holster plate with feed dog, the Hennigan narrow presser foot set, #207 thread top/ #138 thread bottom, size 24 794 7x3 round point needle, and 5-6 stitches per inch.  This setup buries the knots in a single layer of Beta 520 super heavy.  I have also tried #277/#207 thread with needle sizes 27, 26, and 25.   I've done a limited test of cutting point needles but I like the thread tension with round point needles.  I have used the stock holster plate and harness feet that come with the Class 4 for the larger thread and needle sizes.  Still get occasional skipped stitches.

The information for needle choices that I've read in this forum and seen on Youtube is contradictory.  Most suggestions are to use round point needles that are 1-2 sizes larger than what would be used for sewing leather.

I haven't yet tried thread lubricant, and I haven't played with presser foot tension.  I don't notice flagging while sewing.  I mainly sew bridle leather on this machine and would prefer not coating the thread path with lubricant, but I am open to suggestions.

I appreciate your advice on machine setup and best practices for sewing Biothane.